Piezo-electric device



E. W. RUSSEL L ET AL Jan. 10, 192s.

' PIEZO ELECTRIC DEVICE FildMay 1922 a Sheets-Sheet 1 Jan. 10, 1928.1,655,974

. E. w. RUSSELL ET AL.

v PIEZO ELECTRIC-DEVICE- FiiedMay 1. 1922 s Sheets-Sheet 2 a V f m y I fJan. 10, 1928.

1,655,974 E. w. RUSSELL ET AL PIEZO ELECTRIC DEVICE Filed May'l. 1922 3Sheets-Sheet 3 W MM 4 MW .91 2. 6

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Patented Jan. 10, 1928.

PATENT orrlca.

EDWARD W. RUSSELL, OF BEDFORD, AND ARTHUR FREDERICK RICHMOND COTTON, OF

Loy DON, ENGLAND, ASSIGNOBS TO THE CLEVELAND TRUST COMPANY, OF CLEVE-LAND, OHIO, A CORPORATION 01' OHIO.

rmzo-nLncrnIc DEVICE.

Application fled lay 1, 1922, Serial No. 557,641, and in Great Britain.lune 9, 1921 This invention relates to piezo-electric devices andconsists in an improved arran ement for the use of the active crystal,or example of-Rochelle salt, more especially for the reception forreproduction of sound or pressure waves which may be collected in anysuitable manner.

According to the .present invention, the crystal is subjected topressure at each end of an axis, which may or may not be one v of itsaxes of symmetry, and at one or both ends of the said axis it isconnected to a conducting member, the conduction or trans-. mission ofwaves down which is produced by or transmitted to a receiving surface.By the expression conducting member we mean to im 1y a member adapted tothe reasonably e cient conduction of 'mechanical pressure wavesthroughthe material of the said member.

A convenient form of conducting member for applying vibrations orpressure waves to the basal planes of the piezo-electrically activecrystal is found to be a bar or late keptin contact with a basal plane 0the crystal by constant pressure, suitably applied.

conducting members, which extend preferably in diametrically oppositedirections, their operation being produced by or serving to operate thereceiving or transmitting surface through a suitable conductor of waves,

. such as a cross bar arranged diagonally to connect the extremities ofthe arms.

We have discovered that the piezo-electric eifect is independent ofmechanical move- .ment of the members which connect the receiver ofvibrations to the basal planes of the crystal, and may be as efficientlyobtained by the passage of pressure waves through the crystal structure.From this it will be obvious that absolute rigidity of constructionmakes for efliciency and sensitivity, and is of considerable use in theprevention of resonance of the extraneous vibrations in that soundandmusical reproduction for which the apparatus is intended.

We have also found that substances which are insulators to sound arestill capable of a reasonably eflicient conductivity of pressure waves.For example, compressed cellulose acetate not only has this property toor transmitting surface. t

more convenient to apply the pressure from uprights extending from thebase or sides.

Pressure waves when received are conveyed elther directly, or throughthe crossbar, to the conducting members. We have found that the greaterthe cross sectional area ofthese members the greater is theirconductlvlty, up to the saturation point, which is a factor of thecrystal constant. This law has also been found to apply to the cross barsurface and any intermediate conductors.

The invention is hereafter described with l reference to theaccompanying drawings, in The crystal may be mounted between twov whichFigure 1 represents a crystal of the shape which has been found mostsuitable for the present invention.

Figure 2 is a plan of the same.

Figure 3; is a perspective view of the mounted crystal. v Figure 4 showsa device for converting vibrations or pressure waves into electricity orvlce versa.

Figures 5 and 6 are details of one of the conducting members seen inFigure 4..

Figure 7 is an end view of the device showing the cradle mounting.

Figures 8 and 9 represent the application of the invention to atransmitter intended to replace the sound box of a gramophone.

Figure 10 represents a reinforced conducting member for musical sounds.

Figures 11 and 12'illustrate alternative methods of mounting the device.

Figure 13 is a diagram showing the electrical connections when using acondenser for removing needle-scratch and similar noises of gramophonerecords when producing electrical currents by means of a crystal showsthe crystal transmitter such as shown in Figures 8 and 9. v

Crystals of Rochelle salt may be encouraged in a particular hablt ofgrowth to assume the shape illustrated in Figures 1 and 2, in which thesurfaces at a are those referred to as the basal planes. Figure 3contact plates or ands, for example one circumferential band 6 and oneplate 0 at each of the selected bases.

In one manner of carrying the invention into ractice, see Figures 4, 5,6 and 7 a crystal of this kind is mounted between two parallelconducting members (Z which pro ect in diametrically oppositedirections; these conducting members are arran ed at the basal planesand they may be ma e of metal, in which case the separate contact plates0 may be suppressed.

The mounted crystal is supported upon an axis perpendicular to the basalplanes and to the members (1, so that by means of the latter the crystalmay be subjected to pressure waves or its converse effects may bemanifested. It has notbeen found necessary to provide delicate pivotalmounting, any suitable bearing surface belngapplicable.

The conducting members, made in this case of metal and cross-cut orchequered on their adjacent faces, are bedded against the basal planesof the crystal by means of contact pads e of tinfoil or the likeinterleaved with cellulose acetate or similar materlal capable of beingsoftened before assembly so that it will take up the shape of the basalplane of the crystal.

To ensure adequate bearing of the contact surfaces upon the sensitiveregions of the basal planes of the crystal, viz the corners or angles ofthe basal planes, the conducting members (I are recessed as indicated atd in Figures 5 and 6.

Pressure is applied to the crystal through the COIldllCtiIlg members andcontact pads by means of the cradle .f, the open end of which carriesspring plates f which can be adjusted by nuts f to regulate thepressure. These spring plates may be of metal with an intermediate layerf of cellulose acetate or other damping material, and at the oppositeclosed end of the cradle, a bearing plate 7" may be supported likewiseupon a cushion i of cellulose acetate.

The oppositely extending ends of the conducting members (1 are connectedto the receiving or transmitting surface 9 directly or by means of across bar it which is fixed rigidly to the members 03 in any suitablemanner and also connected to the receiving or transmitting surface.

The vibration or pressure waves of the diaphragm 9 will thus betranslated into an alternating effect upon the crystal, producprovidedwith the usual ing an electro-motive force between the contact plates orbands 6, e, which may be utilized for the transmission of currentpossesslecting surfaces directly by means of cross bars or othersuitable connections in conjunction with two collecting surfacesparallel to each other.

Figures 8, 9 and 10 illustrate a form of the apparatus, suitable forconverting the musical sounds or speech represented by the grooves ofthe known type of gramophone or like records, into their electricalequivalents.

The apparatus is conveniently arranged upon a base 7 comprising aframe-work or casing of channel or flat U-section composed of somespringy metal such as duralumin, having attached to the web of thechannel 7 a sheet f of sound insulating material, clamped to the web bya plate 7 of ebonite or the like. The crystal is held between theflanges f of the channel, and is pressed at one end upon a chequeredplate (5' of steel or other suitable material sound-insulated from thebase, for example by a layer of cellulose acetate d with an outer plateof lead (i the latter resting against the inner side of the flange. Thecrystal is clamped between the chequered base d at the one end, and aconducting member d at the other, constant pressure being applied on theconducting member by any suitable means, between two springy flanges fof the U-shaped frame-work.

The conducting member (1 is preferably made of compressed celluloseacetate or other semi-yielding material, which may be reinforced by asuitable proportion of metal (i (see Figure 10) this arrangement servesto convert mechanical vibrations, if any, into pressure waves, to act asan efiicient conductor if already .formed pressure waves are impressed,and to produce the modulating and regulating effect described above. Agramophone needle 71 or its equivalent is placed in one end of themember.

Figure 13 shows the crystal having its circumferential contact band 6and basal contacts 03 0! connected by leads 7' y" respectlvely to thereceiving or amplifying apparatus, represented by head phones in Theleads j j are connected through a variable condenser Z, the function ofwhich is to elimi nate scratching and surface noises of the gramophonerecordm from reproduction in r the receiver k these noises are due tothe roughness of the surface of the record, due

to wear, etc., the sounds caused thereby be mg of a far higher frequencythan the .normal acoustic tones of the record. The piezoelectric deviceacts to convert these noises into electrical oscillations of equivalentfrequency, ,which are readily shunted by the condenser, while therelatively lower frequencies equivalent 'to the normal acoustic tonespass on through the head-phones or amplifier.

The condenser 1 may be adjusted to suit the crystal used and thecondition of the surface of the gramophone record; convenient valuesrange between .001 microfarad and .01 microfarad, depeiiding on thestate of the record surface, the power of the crystal and the ratio ofamplification, but different degrees of surface roughness produceelectrical oscillations of different frequencies, for which reason therange of capacity provided will with advantage be wide, to enable thesame apparatus to function with any record, whatever its condition.

The device is preferably enclosed for protection from externalinfluences; it has been found that stifl paper or thin cardboard j,

' the rece ving or transmitting diaphragm,

and the latter figure showing the mounted crystal as being supportedfrom the base or side of the container.

To obtain the most eflicient results the collecting surface or diaphragmmust be calculated so as to be proportional to the capacity of theconducting. members, whose volume is a factor of the crystal constant.

It is a known fact that pressure waves will travel through -anysubstance to its extremities as in the case of ripples on the surface ofa pond caused by an impact on itssurface, provided the pressure wavesare of sufiicient amplitude to overcome the natural resistance of theconductor.

In cases where the collecting surface or .diaphragm g has to be grippedby its outer edge the pressure waves will tend to pass from thediaphragm to the main frame.

This results in loss of efficiency, and may be prevented by making thecentre more solid, and reducing the thickness, and hence theconductivity of the outer edge. We have effected this most simply bymaking a groove 9' all round the active area between the latter and thegripped edges, as shown in Figures 11 and 12. Increased efficiency maybe obtained by shaping the diaphragm like a magnifying lens, the centreportion 9 being of increased thickness' H 'to the basal .opposite endsof said axis,

planes and centre of the crystal maly be arranged in an suitable manner.

t will be understoo that various modifications may be introduced-in thearrangement described without affecting the principle involved.

' Having thus described our invention, what we claim is e 1. Apiezo-electric device, comprising an active crystal, electrical contactsupon said crystal, means for subjecting said crystal to pressure alongan axis, a conducting member clamped to one of the basal planes of saidcrystal by said pressure means, and means for exerting an oppositetorsional efl'ecteat the other basal plane of said crystal, saidconducting member being constructed of semi-yielding material to conformto the contour of the basal plane of the crystal, said semi-yieldingmaterial being reinforced with metal and adapted to conduct pressurewaves through said basal plane.

2. A piezo-electric device, comprising an active crystal, a contact bandaround the, periphery of said crystal, contact pads at opposite basalplanes of said crystal, said con tact pads composed of metal foilinterleaved with cellulose acetate, electrical connections to saidcontact band and pads respectively, a conducting member, and means forclamping said conducting member against one of said contact pads.

3. A piezo-electric device, comprising an active crystal, electricalcontacts upon said crystal, means for subjecting said crystal topressure along an axis, conducting members clamped to said crystal bysaid pressure at said conducting members extending in diametricallyopposite directions relatively, to said axis, said conducting membersconnected to transmitting surfaces, and semi-yielding means for a theend of the crysta 4. A piezo-electric device, comprising an activecrystal, electrical contacts upon said crystal, a rigid support for saidcrystal, means for subjecting said crystal to axial pressure, means forsubjecting said crystal to pressure, waves at opposite ends of the axisof pressure, and a transmitting surface, said surface bein of lenticularsection having a circumferential groove.

5. A piezo-electric device, comprising an active crystal, electricalcontacts upon said crystal, a support for said crystal, means forsubjecting said crystal to pressure at its basal planes, conductingmembers clamped against said crystal at its basal planes, said membersbeing recessed to insure adequate bearing of said members upon thesensitive regions of the basal planes, a transmitting surface, and

means for conveyin pressure waves between said surface and saiconducting members.

6. Apiezo-electrical device, comprising an active crystal, electricalcontacts upon said crystal, means for subjecting said crystal topressure along an axis, and a conducting member clamped to the basalplane of said crystal at one end of said axis, said member conductingpressure waves through said basal plane and consisting of compressedcellulose acetate reinforced with metal proportioned to theabsorptivecapacity of the crystal used.

7. A piezo-electric device comprising an active crystal, a contact bandaround the periphery of said crystal, torsional arnis at opposite basalplanes of said crystal extending outwardly in opposed directions,contact pads-arranged to conform closely with said asal planes disposedintermediate said planes and said outwardly extending arms, electricalconnections to said contact band and plates respectively, adjustablemeans for exerting pressure axially .of said crystal, and meansconnected to the outer ends of said arms whereby to exert oppositetorsional effects simultaneously upon said basal planes.

8. In a piezo-electric device, in combination, an active crystal,conducting members contacting closely with opposite basal planes of saidcrystal, means for exerting a torsional eifect upon said crystal throughsaid members, means for exertin desired constant pressure axially of saicrystal, electrical connections to said members, and a condenserconnected across the terminals of said crystal, whereby high frequencyelectrical impulses may be shunted.

9. A piezo-electric device, comprising an active crystal, electricalcontacts upon said crystal, a cradle, said cradle supporting saidcrystal, and means for subjecting said crysta to pressure at oppositeplanes of the crystal, said means including a conducting member ofsemi-yielding material reinforced with metal and directly contactingwith a portion of the crystal.

10. In a piezo-el ectric device, in combination, an active crystal,conducting members contacting closely with opposite. planes, of saidcrystal, means for causin pressure to .be exerted upon the crystal, eectrical connections to said conducting members, and a condenserconnected across the electrical terminals of the crystal, whereby highfrequency electrical impulses may be shunted.

In testimony whereof we hereunto afiix our signatures.

EDWARD W. RUSSELL ARTHUR FREDERICK RICHMOND COTTON.

